Multi-articulated link knee joint

ABSTRACT

A multi-articulated link knee joint includes: a knee unit in which an upper link unit rotates relative to a lower link unit by a multi-articulated link mechanism including a plurality of link units including the upper link unit and the lower link unit; a relative position detector for detecting a relative position of the upper link unit relative to the lower link unit; and an angle detector for obtaining a bending angle of the knee unit from the detected relative position.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. § 119 toJapanese Application No. 2018-076109, filed Apr. 11, 2018, the entirecontent of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a multi-articulated link knee joint.

2. Description of the Related Art

Prosthetic legs used by people who had have their thigh cut above theirknee due to a disease or an accident are coupled with an artificial kneejoint that bends like a knee joint of a living body. When the artificialknee joint is bent depending on the motion of the user, motions such asstanding, sitting, and walking are made possible.

Patent document 1 discloses an artificial knee joint including a kneeunit that bends by a multi-articulated link mechanism and an aircylinder that assists the motion of the knee unit depending on thebending angle. In this artificial knee joint, since themulti-articulated link mechanism allows the motion of the knee unit tobe similar to that of the knee joint of a living body, more naturalmotion is made possible. In addition, since walking motion is supportedby a fluid cylinder, the stability of walking is improved.

[Patent document 1] WO2013/132662

The knee joint according to Patent document 1 detects the position of apiston rod connected to the knee unit, and a bending angle of the kneeunit is obtained from the detection result to control an air cylinder.Other than air cylinders or hydraulic cylinders, there are cases whererotary hydraulic dampers having no piston rod are used as auxiliarydrivers for assisting the motion of the knee unit. In this case, thereis a need to change the configuration related to detection of thebending angle. If the configuration related to detection of the bendingangle can be adapted to be compatible with auxiliary drivers ofdifferent types, there is a possibility that cost can be reduced bysharing parts in deploying various product groups.

SUMMARY OF THE INVENTION

The present invention has been made in view of these challenges, and itis an object of the present invention to adapt a configuration fordetecting a bending angle of a knee unit in a multi-articulated linkknee joint to be compatible with auxiliary drivers of a plurality oftypes.

One embodiment of the present invention is a multi-articulated link kneejoint. This multi-articulated link knee joint includes: a knee unit inwhich an upper link unit is rotates relative to a lower link unit by amulti-articulated link mechanism including a plurality of link unitsincluding the upper link unit and the lower link unit; a relativeposition detector for detecting a relative position, relative to acertain link unit among the plurality of link units, of another linkunit; and an angle detector for obtaining a bending angle of the kneeunit from the detected relative position.

According to this embodiment, the relative position of the other linkunit relative to the certain link unit among the plurality of link unitsis detected, and the bending angle of the knee unit is obtained from thedetection result, and thus auxiliary drivers of different types can becovered by similar configurations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a multi-articulated link knee joint accordingto a first embodiment of the present invention;

FIG. 2 is a schematic cross-sectional view of the multi-articulated linkknee joint according to the first embodiment of the present invention;

FIG. 3 is a view illustrating a state in which a knee unit is bent by45° in the multi-articulated link knee joint according to the firstembodiment;

FIG. 4 is a block diagram illustrating a functional configuration of acontrol device;

FIG. 5 is a schematic cross-sectional view of a multi-articulated linkknee joint according to a second embodiment of the present invention;

FIG. 6 is a view illustrating a state in which a knee unit is bent by45° in the multi-articulated link knee joint according to the secondembodiment;

FIG. 7 is a schematic cross-sectional view of a multi-articulated linkknee joint according to a third embodiment of the present invention;

FIG. 8 is a view illustrating a state in which a knee unit is bent by45° in the multi-articulated link knee joint according to the thirdembodiment;

FIG. 9 is a schematic cross-sectional view of a multi-articulated linkknee joint according to a fourth embodiment of the present invention;

FIG. 10 is a view illustrating a state in which a knee unit is bent by45° in the multi-articulated link knee joint according to the fourthembodiment;

FIG. 11 is a diagram for explaining a structure of a relative positiondetector in the multi-articulated link knee joint according to thefourth embodiment;

FIG. 12 is a schematic cross-sectional view of a multi-articulated linkknee joint according to a fifth embodiment of the present invention;

FIG. 13 is a schematic cross-sectional view of a multi-articulated linkknee joint according to a sixth embodiment of the present invention;

FIG. 14 is a graph illustrating an exemplary relationship between thebending angle of a knee unit and the output of an angle sensor;

FIG. 15 is a schematic cross-sectional view of a multi-articulated linkknee joint according to a seventh embodiment of the present invention;

FIG. 16 is a graph illustrating an exemplary relationship between thebending angle of a knee unit and the output of a first angle sensor anda second angle sensor;

FIG. 17 is a table illustrating combinations of sections of the firstangle sensor and sections of the second angle sensor;

FIG. 18A and FIG. 18B are graphs for explaining a method of determiningsections by a turning point;

FIG. 19 is a schematic cross-sectional view of a multi-articulated linkknee joint according to an eighth embodiment of the present invention;and

FIG. 20 is a view illustrating a state in which a knee unit is bent by45° in the multi-articulated link knee joint according to the eighthembodiment.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described by reference to the preferredembodiments. This does not intend to limit the scope of the presentinvention, but to exemplify the invention.

Hereinafter, in embodiments, the same component is denoted by the samesymbol, and redundant explanations are omitted. In addition, forconvenience of explanation, a part of a component is omitted asappropriate in the drawings.

Before specifically explaining a multi-articulated link knee jointaccording to an embodiment, the overview will be explained. Amulti-articulated link knee joint according to an embodiment includes aknee unit in which an upper link unit rotates relative to a lower linkunit by a multi-articulated link mechanism and an auxiliary driver forassisting the motion of the knee unit. An example of the auxiliarydriver is a rotary hydraulic damper. The multi-articulated link kneejoint includes a relative position detector that detects a relativeposition, relative to a certain link unit among a plurality of linkunits, of another link unit. This relative position may be, for example,a distance from the certain link unit to the other link unit, a rotationangle of the other link unit to the certain link unit, and so on. Thebending angle of the knee unit can be obtained from the detectedrelative position. The auxiliary driver may be a cylinder device such asan air cylinder or a hydraulic cylinder. According to a knee jointaccording to the present embodiment, auxiliary drivers of differenttypes can be covered by similar configurations to detect the bendingangle of a knee unit.

First Embodiment

FIG. 1 is a side view of a multi-articulated link knee joint 100according to a first embodiment of the present invention. FIG. 2 is aschematic cross-sectional view of the multi-articulated link knee joint100 according to the first embodiment of the present invention. In thefollowing description, in an xyz orthogonal coordinate systemillustrated in each drawing, a direction parallel to the x axis isdefined as the lateral direction, and the positive direction of the xaxis is referred to as “left” with the negative direction referred to as“right.” A direction parallel to the y axis is defined as theanterior-posterior direction, and the positive direction of the y axisis referred to as “anterior” with the negative direction referred to as“posterior.” A direction parallel to the z axis is defined as thevertical direction, and the positive direction of the z axis is referredto as “up” with the negative direction referred to as “down.”

The multi-articulated link knee joint 100 includes a knee unit 10. Theknee unit 10 is bent by a multi-articulated link mechanism having aplurality of link units. In the first embodiment, the multi-articulatedlink mechanism is a four-articulated link mechanism including four linkunits of an upper link unit 50, a lower link unit 52, an anterior linkunit 54, and a posterior link unit 56. In this specification, a link andparts secured to the link to move in conjunction with the link arecollectively referred to as a “link unit.” The upper link unit 50includes an upper link 16 and a thigh connector 32. The lower link unit52 includes a lower link 18 and an lower leg part 12. The anterior linkunit 54 includes an anterior link 20. The posterior link unit 56includes a posterior link 22.

The upper link 16 is provided with a first shaft 24 and a second shaft26, and the lower link 18 is provided with a third shaft 28 and a fourthshaft 30. Each of the shafts is provided such that the axial directionthereof is parallel to the x axis and so as to be rotatable. Theanterior link 20 is attached to the ends of the first shaft 24 and thethird shaft 28. The posterior link 22 is attached to the ends of thesecond shaft 26 and the fourth shaft 30. The upper link 16 is supportedby the anterior link 20 and the posterior link 22 and rotates relativeto the lower link 18.

The lower leg part 12 is formed in a cylindrical shape and is securedunder the lower link 18. Furthermore, provided under the lower leg part12 is a leg connector 40 which is connected to a leg part included in aprosthetic leg.

The thigh connector 32 protruding from the upper link 16 is connected toa socket attached to the thigh of a user. An angle formed by thedirection in which the thigh connector 32 protrudes and the z axis isdefined as the bending angle of the knee unit 10. The bending angleillustrated in FIG. 1 and FIG. 2 is 0°, which is a state in which theknee unit 10 is completely extended.

FIG. 3 is a view illustrating a state in which the knee unit 10 is bentby 45° in the multi-articulated link knee joint 100 according to thefirst embodiment. When the bending angle is large, the anterior link 20and the posterior link 22 intersect. The upper link 16 rotates whilemoving backward relative to the lower link 18. Due to the rotation ofthe upper link 16, the knee unit 10 bends like the knee joint of aliving body does.

The multi-articulated link knee joint 100 further includes a relativeposition detector 58 for detecting the relative position of the upperlink unit 50 relative to the lower link unit 52. The relative positiondetector 58 includes a magnet 60 and a magnetic sensor 62 for detectingthe intensity of the magnetic field generated by the magnet 60. Themagnet 60 may be, for example, a rectangular alnico magnet. The magneticsensor 62 may be, for example, a Hall element. The magnetic sensor 62 isprovided at a predetermined portion of the lower link 18, for example,on the lower link 18. The magnet 60 is provided at a predeterminedportion of the upper link 16, for example, at a portion that approachesclose to the magnetic sensor 62 when the bending angle is 0°. The magnet60 is arranged such that the N pole faces the magnetic sensor 62 and theS pole faces the opposite side to the magnetic sensor 62 when thebending angle of the knee unit 10 is 0°.

The magnetic sensor 62 provided at the lower link 18 outputs a detectionvalue corresponding to the distance d to the magnet 60 provided at theupper link 16. The intensity of the magnetic field formed by the magnet60 decreases as the distance from the magnet 60 increases. Asillustrated in FIG. 2, when the bending angle of the knee unit 10 is 0°,the distance d between the magnet 60 and the magnetic sensor 62 is thesmallest, and the detection value of the magnetic sensor 62 is thelargest at this time. As illustrated in FIG. 3, as the bending angle ofthe knee unit 10 increases, the distance d increases, and thus thedetection value of the magnetic sensor 62 decreases.

The multi-articulated link knee joint 100 further includes a controldevice 14. The control device 14 is accommodated in the lower leg part12. The control device 14 receives a detection value of the relativeposition detector 58 (that is, a detection value of the magnetic sensor62), obtains the bending angle of the knee unit 10 from the detectionvalue, and controls an auxiliary driver (not illustrated).

FIG. 4 is a block diagram illustrating a functional configuration of thecontrol device 14. Each of the blocks illustrated herein in the blockdiagram can be implemented by an element or a mechanical deviceincluding a CPU of a computer from the perspectives of hardware and,from the perspectives of software, by a computer program or the like. Inthis example, functional blocks implemented by coordination thereof areillustrated. Therefore, it should be understood by a person skilled inthe art that these functional blocks can be implemented by various formsby hardware, software, or a combination thereof.

The control device 14 includes an angle detector 42 and a controller 44.The angle detector 42 obtains the bending angle of the knee unit 10 froma detection value of the relative position detector 58. For example,when a table is generated in advance by measuring the relationshipbetween the bending angle of the knee unit 10 and the detection value ofthe relative position detector 58, a bending angle of the knee unit 10can be obtained from a detection value of the relative position detector58 by referring to the table.

The controller 44 controls an auxiliary driver 46 in accordance with thebending angle obtained by the angle detector 42. In the presentembodiment, the auxiliary driver 46 is a rotary hydraulic damperattached to the first shaft 24 and is controlled by the controller 44 toassist the motion of the knee unit 10. The controller 44 controls theauxiliary driver 46 so as to limit the rotation of the third shaft 28when the bending angle is close to 0°. This prevents knee bending, thatis, the knee unit 10 bent against the will of the user. In addition,when the leg is in a swinging state in which the bending angle changessuch as when walking, the auxiliary driver 46 is controlled so as torotate the third shaft 28 in accordance with the angle-changingdirection. As a result, the lower leg part 12 swings in accordance withkicking-out of the leg, and thus the user can walk comfortably. Notethat the rotary hydraulic damper serving as the auxiliary driver 46 maybe provided at any one of the second shaft 26, the third shaft 28, andthe fourth shaft 30. However, since there are times that the rotationdirection of the third shaft 28 and the fourth shaft 30 is reversedduring rotation of the upper link 16, the rotary hydraulic damper ismore easily controlled when provided at the first shaft 24 or the secondshaft 26 that rotates always in the same direction as the upper link 16does. Alternatively, a cylinder device such as an air cylinder or ahydraulic cylinder may be provided as the auxiliary driver 46.

The usage and operation according to the above configuration are asfollows. The multi-articulated link knee joint 100 is used while thethigh connector 32 is connected to a socket attached to the thigh of theuser with the leg part connected to the leg connector 40. The knee unit10 bends when the upper link 16 rotates relative to the lower link 18 bythe multi-articulated link mechanism. When the knee unit 10 is bent, theangle detector 42 obtains the bending angle from the detection value ofthe relative position detector 58. The controller 44 controls theauxiliary driver in accordance with the bending angle to assist themotion of the knee unit 10.

In the multi-articulated link knee joint 100 according to the firstembodiment, since the relative position detector 58 including the magnet60 and the magnetic sensor 62 is included in the knee unit 10, even withauxiliary drivers of different types, the bending angle of the knee unit10 can be detected. In deploying various product groups, theconfiguration for detecting the bending angle can be shared to reducethe manufacturing cost.

In the multi-articulated link knee joint 100 according to the firstembodiment, both the magnetic sensor 62 of the relative positiondetector 58 and the angle detector 42 (control device 14) are providedat the lower link unit 52. Since the angle detector 42 obtains thebending angle of the knee unit 10 from the detection result of themagnetic sensor 62, in order to transmit detection information of themagnetic sensor 62 to the angle detector 42, it is necessary that themagnetic sensor 62 and the angle detector 42 be connected by wiring. Inthe case where the magnetic sensor 62 and the angle detector 42 areprovided at separate portions that are displaced from each other, it isnecessary to adopt a structure that does not cause a failure such asdisconnection in the wiring. This is not preferable since this leads toincreased cost of the knee joint. In the multi-articulated link kneejoint 100 according to the first embodiment, since the magnetic sensor62 and the angle detector 42 (the control device 14) are provided at thesame lower link unit 52, the wiring can be made simple, which results incost reduction of the knee joint.

Second Embodiment

In the first embodiment, the relative position detector 58 detects thedistance d between the magnet 60 provided at the upper link 16 and themagnetic sensor 62 provided at the lower link 18 and thereby detects therelative position of the upper link unit 50 relative to the lower linkunit 52. However, the relative position detector 58 may not only detectthe relative position of the upper link unit 50 relative to the lowerlink unit 52, but may also detect the relative position of another linkunit relative to a certain link unit among the four link units. In asecond embodiment, an example as such will be described.

FIG. 5 is a schematic cross-sectional view of a multi-articulated linkknee joint 200 according to the second embodiment of the presentinvention. In the multi-articulated link knee joint 200 illustrated inFIG. 5, the bending angle of a knee unit 10 is 0°. FIG. 6 is a viewillustrating a state in which the knee unit 10 is bent by 45° in themulti-articulated link knee joint 200 according to the secondembodiment.

The multi-articulated link knee joint 200 differs from themulti-articulated link knee joint 100 according to the first embodimentin that a magnetic sensor 62 of a relative position detector 58 isprovided at an anterior link 20. The magnet 60 is provided at apredetermined portion of the upper link 16, for example, at a portionthat approaches close to the magnetic sensor 62 when the bending angleis 0°. Therefore, in the second embodiment, the relative positiondetector 58 including the magnet 60 and the magnetic sensor 62 detectsthe relative position of the upper link unit 50 relative to the anteriorlink unit 54.

The magnetic sensor 62 provided at the anterior link 20 outputs adetection value corresponding to the distance d to the magnet 60provided at the upper link 16. The intensity of the magnetic fieldformed by the magnet 60 decreases as the distance from the magnet 60increases. As illustrated in FIG. 5, when the bending angle of the kneeunit 10 is 0°, the distance d between the magnet 60 and the magneticsensor 62 is the smallest, and the detection value of the magneticsensor 62 is the largest at this time. As illustrated in FIG. 6, as thebending angle of the knee unit 10 increases, the distance d increases,and thus the detection value of the magnetic sensor 62 decreases.

Also in the multi-articulated link knee joint 200 according to thesecond embodiment, the bending angle of the knee unit 10 is obtained onthe basis of the detection value of the relative position detector 58,and an auxiliary driver (not illustrated) is controlled in accordancewith the obtained bending angle. Since the relative position detector 58including the magnet 60 and the magnetic sensor 62 is provided at theknee unit 10, even with auxiliary drivers of different types, thebending angle of the knee unit 10 can be detected.

Third Embodiment

FIG. 7 is a schematic cross-sectional view of a multi-articulated linkknee joint 300 according to a third embodiment of the present invention.In the multi-articulated link knee joint 300 illustrated in FIG. 7, thebending angle of a knee unit 10 is 0°. FIG. 8 is a view illustrating astate in which the knee unit 10 is bent by 45° in the multi-articulatedlink knee joint 300 according to the third embodiment.

The multi-articulated link knee joint 300 is different from themulti-articulated link knee joint 100 according to the first embodimentin the structure of the relative position detector. A relative positiondetector 358 of the multi-articulated link knee joint 300 includes amagnet 360 and a magnetic sensor 362 that detects the intensity of themagnetic field generated by the magnet 360. The magnetic sensor 362 maybe, for example, a Hall element. The magnetic sensor 362 is provided ata predetermined portion of a lower link 18, for example, on the lowerlink 18.

In the third embodiment, the magnet 360 is a bar magnet extending in anarc shape in the rotation direction of an upper link 16. The magnet 360is arranged such that the N pole faces the magnetic sensor 362 and the Spole faces the opposite side to the magnetic sensor 362. In FIG. 7,symbol “C” indicates the center of the magnet 360 extending in the arcshape. The center C of the arc-shaped magnet 360 is eccentric anteriorlywith respect to the center of a first shaft 24 which is the rotationaxis of the upper link 16, and thus the distance d between the magnet360 and the magnetic sensor 362 varies as the bending angle of the kneeunit 10 varies.

The magnetic sensor 362 provided at the lower link 18 outputs adetection value corresponding to the distance d to the magnet 360provided at the upper link 16. The intensity of the magnetic fieldformed by the magnet 360 decreases as the distance from the magnet 360increases. As illustrated in FIG. 7, when the bending angle of the kneeunit 10 is 0°, the distance d is the smallest, and the detection valueof the magnetic sensor 362 is the largest at this time. As illustratedin FIG. 8, as the bending angle of the knee unit 10 increases, thedistance d increases, and thus the detection value of the magneticsensor 362 decreases.

Also in the multi-articulated link knee joint 300 according to the thirdembodiment, the bending angle of the knee unit 10 is obtained on thebasis of the detection value of the relative position detector 358, andan auxiliary driver (not illustrated) is controlled in accordance withthe obtained bending angle. Since the relative position detector 358including the magnet 360 and the magnetic sensor 362 is provided at theknee unit 10, even with auxiliary drivers of different types, thebending angle of the knee unit 10 can be detected.

In the multi-articulated link knee joint 300 according to the thirdembodiment, since the magnetic sensor 362 and an angle detector (controldevice 14) are provided at the same lower link unit 52, the wiring canbe made simple, which results in cost reduction of the knee joint.

Moreover, in the multi-articulated link knee joint 300 according to thethird embodiment, the arc-shaped bar magnet is adopted as the magneticsensor 362 in the relative position detector 358. Therefore, as comparedwith the case where the square magnet 60 is used as in the first andsecond embodiments described above, a strong magnetic field can beformed around the magnetic sensor 362 even when the bending angleincreases. As a result, the detection accuracy of the relative positiondetector 358 can be enhanced as compared with the first and secondembodiments, and moreover, the detection range of the bending angle canbe broadened.

Fourth Embodiment

FIG. 9 is a schematic cross-sectional view of a multi-articulated linkknee joint 400 according to a fourth embodiment of the presentinvention. In the multi-articulated link knee joint 400 illustrated inFIG. 9, the bending angle of a knee unit 10 is 0°. FIG. 10 is a viewillustrating a state in which the knee unit 10 is bent by 45° in themulti-articulated link knee joint 400 according to the fourthembodiment.

The multi-articulated link knee joint 400 also differs from themulti-articulated link knee joint 100 according to the first embodimentin the structure of the relative position detector. FIG. 11 is a diagramfor explaining a structure of a relative position detector 458 in themulti-articulated link knee joint 400 according to the fourthembodiment. The relative position detector 458 includes a first magnet460, a second magnet 461, and a magnetic sensor 462 that detects theintensity of the magnetic field generated by the first magnet 460 andthe second magnet 461, and detects the relative position of an upperlink unit 50 relative to the lower link unit 52. The magnetic sensor 462may be, for example, a Hall element. The magnetic sensor 462 is providedat a predetermined portion of a lower link 18, for example, on the lowerlink 18.

The first magnet 460 and the second magnet 461 are bar magnets extendingin an arc shape in the rotation direction of an upper link 16. Asillustrated in FIG. 9, the center C of the arc-shaped first magnet 460and the second magnet 461 is eccentric anteriorly with respect to thecenter of a first shaft 24 which is the rotation axis of the upper link16, and thus the distance d between the first magnet 460 and the secondmagnet 461 and the magnetic sensor 462 varies as the bending angle ofthe knee unit 10 varies.

As illustrated in FIG. 11, the first magnet 460 and the second magnet461 are arranged such that the S pole of the first magnet 460 and the Npole of the second magnet 461 face each other. In FIG. 11, the magneticfield formed by the first magnet 460 and the second magnet 461 isillustrated. The intensity of the magnetic field formed by the firstmagnet 460 and the second magnet 461 decreases as the distance from thefirst magnet 460 and the second magnet 461 increases. As illustrated inFIG. 9, when the bending angle of the knee unit 10 is 0°, the distance dis the smallest, and the detection value of the magnetic sensor 462 isthe largest at this time. As illustrated in FIG. 10, as the bendingangle of the knee unit 10 increases, the distance d increases, and thusthe detection value of the magnetic sensor 462 decreases.

Also in the multi-articulated link knee joint 400 according to thefourth embodiment, the bending angle of the knee unit 10 is obtained onthe basis of the detection value of the relative position detector 358,and an auxiliary driver (not illustrated) is controlled in accordancewith the obtained bending angle. Since the relative position detector458 including the first magnet 460, the second magnet 461, and themagnetic sensor 462 is provided at the knee unit 10, even with auxiliarydrivers of different types, the bending angle of the knee unit 10 can bedetected.

In the multi-articulated link knee joint 400 according to the fourthembodiment, since the magnetic sensor 462 and an angle detector (controldevice 14) are provided at the same lower link unit 52, the wiring canbe made simple, which results in cost reduction of the knee joint.

Furthermore, in the multi-articulated link knee joint 400 according tothe fourth embodiment, the first magnet 460 and the second magnet 461are arranged to face each other in the relative position detector 458,which allows an even stronger magnetic field to be formed as comparedwith the case of using the single magnet 360 as in the third embodimentdescribed above. As a result, the detection accuracy of the relativeposition detector 458 can be further enhanced as compared with the thirdembodiment, and moreover, the detection range of the bending angle canbe broadened.

Fifth Embodiment

FIG. 12 is a schematic cross-sectional view of a multi-articulated linkknee joint 500 according to a fifth embodiment of the present invention.In the multi-articulated link knee joint 500 illustrated in FIG. 12, thebending angle of a knee unit 10 is 0°.

The multi-articulated link knee joint 500 is different from themulti-articulated link knee joint 100 according to the first embodimentin the structure of the relative position detector. A relative positiondetector 558 of the multi-articulated link knee joint 500 includes agroove 560 formed in an upper link 16 and a distance sensor 562 providedat a lower link 18. The relative position detector 558 detects therelative position of an upper link unit 50 relative to a lower link unit52.

The groove 560 is formed on the outer circumferential surface of theupper link 16 on the lower link 18 side so as to extend in an arc shapealong the rotation direction of the upper link 16. The groove 560 isformed such that the depth varies along the extending direction. In FIG.12, symbol “C” indicates the center of the groove 560 extending in anarc shape. As illustrated in FIG. 12, the center C of the groove 560 iseccentric anteriorly with respect to the center of a first shaft 24which is the rotation axis of the upper link 16. With this structure,when the bending angle of the knee unit 10 is 0°, the depth of thegroove 560 increases as it extends posteriorly.

The distance sensor 562 detects the distance d to the bottom of thegroove 560, and may be, for example, an infrared sensor or an ultrasonicsensor. Since the depth of the groove 560 increases as it extendsposteriorly as described above, the detection value of the distancesensor 562 (that is, distance d) is the smallest when the bending angleof the knee unit 10 is 0° as illustrated in FIG. 12, and the detectionvalue of the distance sensor 562 increases when the bending angle of theknee unit 10 increases.

An angle detector 42 (see FIG. 4) of the control device 14 obtains thebending angle of the knee unit 10 from the detection value of therelative position detector 558 (that is, the detection value of thedistance sensor 562). For example, when a table is generated in advanceby measuring the relationship between the bending angle of the knee unit10 and the detection value of the relative position detector 558, abending angle of the knee unit 10 can be obtained from a detection valueof the relative position detector 558 by referring to the table.

Also in the multi-articulated link knee joint 500 according to the fifthembodiment, the bending angle of the knee unit 10 is obtained on thebasis of the detection value of the relative position detector 558, andan auxiliary driver (not illustrated) is controlled in accordance withthe obtained bending angle. Since the relative position detector 558including the groove 560 and the distance sensor 562 is provided at theknee unit 10, even with auxiliary drivers of different types, thebending angle of the knee unit 10 can be detected.

In the multi-articulated link knee joint 500 according to the fifthembodiment, since the distance sensor 562 and an angle detector (controldevice 14) are provided at the same lower link unit 52, the wiring canbe made simple, which results in cost reduction of the knee joint.

Sixth Embodiment

FIG. 13 is a schematic cross-sectional view of a multi-articulated linkknee joint 600 according to a sixth embodiment of the present invention.In the multi-articulated link knee joint 600 illustrated in FIG. 13, thebending angle of a knee unit 10 is 0°. Unlike the above embodiments, inthe multi-articulated link knee joint 600 according to the sixthembodiment, the rotation angle of an upper link unit 50 with respect toan anterior link unit 54 (that is, rotation angle about a first shaft24) is detected, and the bending angle of the knee unit 10 is obtainedon the basis of the detection result.

The multi-articulated link knee joint 600 includes an angle sensor 658that detects the rotation angle about the first shaft 24 of the upperlink 16 as a relative position detector. The angle sensor 658 isprovided at a first shaft 24. As the angle sensor 658, for example, apotentiometer, a rotary encoder, a resolver, or the like can be used.

FIG. 14 illustrates an example of the relationship between the bendingangle θ of the knee unit 10 and the output (detection value) of theangle sensor 658. In the example illustrated in FIG. 14, as the bendingangle θ of the knee unit 10 increases, the output of the angle sensoralso increases. Since the bending angle θ of the knee unit 10 and theoutput of the angle sensor 658 correspond on one-to-one basis, thebending angle of the knee unit 10 can be obtained from the output of theangle sensor 658. Then, an auxiliary driver (not illustrated) iscontrolled in accordance with the obtained bending angle of the kneeunit 10.

Also in the multi-articulated link knee joint 600 according to the sixthembodiment, since the angle sensor 658 as the relative position detectoris provided at the knee unit 10, even with auxiliary drivers ofdifferent types, the bending angle of the knee unit 10 can be detected.

In the sixth embodiment, the angle sensor 658 is provided at the firstshaft 24; however, an angle sensor may be provided at a second shaft 26to detect the rotation angle of the upper link unit 50 with respect to aposterior link unit 56 (that is, rotation angle about the second shaft26) may be detected. Even in the case where an angle sensor is providedat the second shaft 26, the bending angle θ of the knee unit 10 and theoutput of the angle sensor correspond on one-to-one basis, and thus thebending angle of the knee unit 10 can be obtained from the output of theangle sensor.

Seventh Embodiment

FIG. 15 is a schematic cross-sectional view of a multi-articulated linkknee joint 700 according to a seventh embodiment of the presentinvention. In the multi-articulated link knee joint 700 illustrated inFIG. 15, the bending angle of the knee unit 10 is 0°. In themulti-articulated link knee joint 700 according to the seventhembodiment, rotation angles of an anterior link unit 54 and a posteriorlink unit 56 with respect to a lower link unit 52 (that is, rotationangles about a third shaft 28 and a fourth shaft 30) are detected, andthe bending angle of the knee unit 10 is detected on the basis of thedetection results.

The multi-articulated link knee joint 700 includes, as a relativeposition detector, a first angle sensor 758 for detecting the rotationangle of an anterior link 20 about the third shaft 28 and a second anglesensor 759 for detecting the rotation angle about the fourth shaft 30 ofa posterior link 22. The first angle sensor 758 is provided at the thirdshaft 28, and the second angle sensor 759 is provided at the fourthshaft 30. As the first angle sensor 758 and the second angle sensor 759,for example, potentiometers, rotary encoders, resolvers, or the like canbe used.

In the multi-articulated link knee joint 700 according to the seventhembodiment, an angle detector 42 (see FIG. 4) of the control device 14obtains the bending angle on the basis of the output of the first anglesensor 758 and the second angle sensor 759.

FIG. 16 illustrates an example of the relationship between the bendingangle θ of the knee unit 10 and the output (detection values) of thefirst angle sensor 758 and the second angle sensor 759. In a first shaft24 and a second shaft 26 provided at an upper link 16 in afour-articulated link mechanism, the output of an angle sensor and thebending angle of a knee unit 10 correspond on one-to-one basis; howeverin a third shaft 28 and a fourth shaft 30 provided to a lower link 18,the output of the angle sensor and the bending angle of the knee unit 10do not correspond on one-to-one basis. That is, in the third shaft 28and the fourth shaft 30, there are two different bending angles for thesame angle sensor output. As illustrated in FIG. 16, an output curve ofthe first angle sensor 758 provided at the third shaft 28 has a turningpoint at a bending angle of θ=B1, and the second angle sensor 759provided at the fourth shaft 30 has a turning point at a bending angleof θ=B2. This is because the four-articulated link mechanism reaches adead point as deformation progresses, and then each of the links move indifferent directions. Therefore, it is difficult to obtain the bendingangle only from the output of the first angle sensor 758 or only fromthe output of the second angle sensor 759. Therefore, in the seventhembodiment, the bending angle is obtained utilizing both the first anglesensor 758 and the second angle sensor 759.

Hereinafter, a method of obtaining the bending angle θ using the outputof the first angle sensor 758 and the output of the second angle sensor759 will be described. Let an angle sensor output when the bending angleθ of the knee unit 10 is 0° be the point zero. Each of the output curvesof the first angle sensor 758 and the second angle sensor 759 is dividedinto a section (let this be section “0”) having a bending angle smallerthan the turning point and a section having a bending angle larger thanthe turning point (let this be section “1”) (see FIG. 16).

FIG. 17 is a table illustrating combinations of the sections of thefirst angle sensor 758 and the sections of the second angle sensor 759.By combining the sections “0” and “1” of the first angle sensor 758 andthe sections “0” and “1” of the second angle sensor 759, the followingthree groups are formed. For each of the groups, a relational expressionof the angle sensor output and the bending angle θ is given.

(1) Group of θ<B1 (section “0” for the first angle sensor 758 andsection “0” for the second angle sensor 759)

(2) Group of B1<θ<B2 (section “1” for the first angle sensor 758 andsection “0” for the second angle sensor 759)

(3) Group of B2<θ (section “1” for the first angle sensor 758 andsection “1” for the second angle sensor 759)

At the time of actual control, an angle detector 42 (see FIG. 4) of acontrol device 14 determines from the output of the first angle sensor758 and the second angle sensor 759 which one of the above three groupsthe bending angle θ belongs to.

FIG. 18A and FIG. 18B are graphs for explaining a method of determiningsections by a turning point. When the output of the first angle sensor758 reaches the turning point (the point where the output changes froman increase to a decrease or from a decrease to an increase), a sectionfor the first angle sensor 758 is determined from an increase/decreaseof the second angle sensor 759. For example in FIG. 18A, in the casewhere the first angle sensor 758 has a decrease near the turning pointand the second angle sensor 759 has an increase, section “1” is obtainedfor the first angle sensor 758, and section “0” is obtained for thesecond angle sensor 759. Thus, it can be determined that the bendingangle belongs to the group of B1<θ<B2.

Moreover, when the output of the second angle sensor 759 reaches theturning point, a section for the second angle sensor 759 is determinedfrom an increase/decrease of the first angle sensor 758. For example inFIG. 18B, in the case where the second angle sensor 759 has a decreasenear the turning point and the first angle sensor 758 has an increase,section “1” is obtained for the first angle sensor 758, and section “1”is obtained for the second angle sensor 759. Thus, it can be determinedthat the bending angle belongs to the group of B2<θ.

After determining the group to which the bending angle θ belongs, theangle detector 42 obtains the bending angle θ using the relationalexpression between the angle sensor output given to the group to whichthe bending angle θ belongs and the bending angle θ. As described above,by determining the group to which the bending angle θ belongs andapplying different relational expressions for each of the groups, thebending angle can be obtained even with the first angle sensor 758 andthe second angle sensor 759 output of which having turning points

It is desirable that the “point zero” of the angle sensor outputdescribed above be determined on the basis of the second angle sensor759. As understood from FIG. 16, since for the first angle sensor 758there is another bending angle θ, at which the same output value as thatof the point zero is obtained, other than the bending angle of θ=0°, thepoint at which the bending angle θ equals 0° cannot be determined. Onthe other hand, since for the second angle sensor 759 there is nobending angle θ, at which the same output value as that of the pointzero is obtained, other than the bending angle of θ=0°, the point atwhich the bending angle θ equals 0° can be determined uniquely.

Also in the multi-articulated link knee joint 700 according to theseventh embodiment, an auxiliary driver (not illustrated) is controlledin accordance with the obtained bending angle. Since the first anglesensor 758 and the second angle sensor 759 as the relative positiondetector are provided at the knee unit 10, even with auxiliary driversof different types, the bending angle of the knee unit 10 can bedetected.

In the multi-articulated link knee joint 700 according to the seventhembodiment, since the first angle sensor 758, the second angle sensor759, and the angle detector (control device 14) are provided at the samelower link unit 52, the wiring can be made simple, which results in costreduction of the knee joint.

Eighth Embodiment

FIG. 19 is a schematic cross-sectional view of a multi-articulated linkknee joint 800 according to an eighth embodiment of the presentinvention. In the multi-articulated link knee joint 800 illustrated inFIG. 19, the bending angle of the knee unit 10 is 0°. Themulti-articulated link knee joint 800 according to the seventhembodiment includes a first acceleration sensor 860 and a secondacceleration sensor 862 as a relative position detector. The firstacceleration sensor 860 is provided at an upper link 16, and the secondacceleration sensor 862 is provided at a lower link 18. In the eighthembodiment, the relative position of an upper link unit 50 relative to alower link unit 52 is detected using the first acceleration sensor 860and the second acceleration sensor 862.

The first acceleration sensor 860 has a reference axis A1 and detects anangle D1 formed between the reference axis A1 and a direction of thegravitational acceleration g (vertical direction). When the bendingangle of the knee unit 10 is 0° and the central axis Ax of an lower legpart 12 is parallel to the vertical direction, the first accelerationsensor 860 is arranged such that the reference axis A1 is oriented inthe vertical direction. At this time, the angle D1 detected by the firstacceleration sensor 860 is 0°. Similarly, the second acceleration sensor862 has a reference axis A2 and detects an angle Φ2 formed between thereference axis A2 and a direction of the gravitational acceleration g(vertical direction). When the bending angle of the knee unit 10 is 0°and the central axis Ax of the lower leg part 12 is parallel to thevertical direction, the second acceleration sensor 862 is arranged suchthat the reference axis A2 is oriented in the vertical direction. Atthis time, the angle Φ2 detected by the second acceleration sensor 862is 0°.

FIG. 20 is a view illustrating a state in which the knee unit 10 is bentby 45° in the multi-articulated link knee joint 800 according to theeighth embodiment. FIG. 20 illustrates a state of the multi-articulatedlink knee joint 800 during walking, and the central axis Ax of the lowerleg part 12 is inclined with respect to the vertical direction.

In the state illustrated in FIG. 20, the first acceleration sensor 860provided at the upper link 16 detects an angle Φ1 formed between thereference axis A1 and the vertical direction. In addition, the secondacceleration sensor 862 provided at the lower link 18 detects an angleΦ2 formed between the reference axis A2 and the vertical direction. Theinformation of the angles Φ1 and Φ2 detected by the first accelerationsensor 860 and the second acceleration sensor 862 is sent to a controldevice 14. An angle detector 42 (see FIG. 4) of the control device 14obtains the bending angle θ of the knee unit 10 on the basis of theangles Φ1 and Φ2. As can be seen from FIG. 20, the bending angle θ isobtained from the following mathematical formula:

θ=Φ2−Φ1.

Also in the multi-articulated link knee joint 800 according to theeighth embodiment, an auxiliary driver (not illustrated) is controlledin accordance with the obtained bending angle. Since the firstacceleration sensor 860 and the second acceleration sensor 862 as therelative position detector are provided at the knee unit 10, even withauxiliary drivers of different types, the bending angle of the knee unit10 can be detected.

In the eighth embodiment, the first acceleration sensor 860 and thesecond acceleration sensor 862 may be used in conjunction with anangular velocity sensor (gyroscope). In this case, more accurate angledetection can be performed.

The present invention has been described above on the basis of theembodiments. The embodiments are merely examples, and thus it should beunderstood by a person skilled in the art that combinations ofcomponents or processing processes of the examples may include variousvariations and that such variations are also within the scope of thepresent invention.

In the present specification, the present invention has been describedwith the example of multi-articulated link knee joint having four axes.However, the present invention is also applicable to a uniaxial kneejoint. Specifically, the method of detecting the bending angle of theknee unit described in the first embodiment, the third embodiment, thefourth embodiment, the fifth embodiment, and the eighth embodimentdescribed above is also applicable to a uniaxial knee joint.

What is claimed is:
 1. A multi-articulated link knee joint comprising: aknee unit in which an upper link unit is structured to rotate relativeto a lower link unit by a multi-articulated link mechanism including aplurality of link units including the upper link unit and the lower linkunit; a relative position detector structured to detect a relativeposition, relative to a certain link unit among the plurality of linkunits, of another link unit; and an angle detector structured to obtaina bending angle of the knee unit from the detected relative position. 2.The multi-articulated link knee joint according to claim 1, wherein therelative position detector detects a distance from the certain link unitto the other link unit as the relative position, and the angle detectorobtains a bending angle of the knee unit from the detected distance. 3.The multi-articulated link knee joint according to claim 2, wherein therelative position detector includes: a magnet provided at the certainlink unit; and a magnetic sensor provided at the other link unit, themagnetic sensor structured to detect an intensity of a magnetic fieldgenerated by the magnet.
 4. The multi-articulated link knee jointaccording to claim 3, wherein the magnet is provided at the upper linkunit, and the magnetic sensor is provided at the lower link unit.
 5. Themulti-articulated link knee joint according to claim 4, wherein themagnet has an arc shape extending in a rotation direction of the upperlink unit, and a center of the arc shape is eccentric with respect to arotation axis of the upper link unit.
 6. The multi-articulated link kneejoint according to claim 5, wherein the magnet includes a first magnetand a second magnet of an arc shape arranged so as to face each other.7. The multi-articulated link knee joint according to claim 1, whereinthe relative position detector detects a rotation angle of the otherlink unit with respect to the certain link unit as the relativeposition, and the angle detector obtains a bending angle of the kneeunit from the detected rotation angle.
 8. The multi-articulated linkknee joint according to claim 1, wherein the multi-articulated linkmechanism comprises an anterior link unit and a posterior link unitrotatably supporting the upper link unit with respect to the lower linkunit, the relative position detector detects a rotation angle of each ofthe anterior link unit and the posterior link unit with respect to thelower link unit as the relative position, and the angle detector obtainsa bending angle of the knee unit from the detected rotation angles ofthe anterior link unit and the posterior link unit.
 9. Themulti-articulated link knee joint according to claim 1, wherein therelative position detector comprises: a first acceleration sensorprovided at the upper link unit; and a second acceleration sensorprovided at the lower link unit, wherein the angle detector obtains abending angle of the knee unit on the basis of detection results of thefirst acceleration sensor and the second acceleration sensor.